Test unit for use at a network interface device

ABSTRACT

A test unit provides testing capability at a network interface device (NID). The test unit may be remotely activated so that testing is initiated upon activation from a remote site. In one embodiment, a characteristic signal is sent over a telephone line toward the NID. A characteristic signal is detected and the testing unit is activated. The testing unit may perform multiple types of tests, including tests for detecting line loss, line noise and latency. The test may be implemented using electronic circuitry or using an intelligent computer system.

TECHNICAL FIELD

[0001] The present invention relates generally to telecommunicationsystems and more particularly to a test unit for use at a networkinterface device, including long distance lines, local lines andsubscriber equipment.

BACKGROUND OF THE INVENTION

[0002] The United States Public Switched Telephone Network (PSTN)includes a number of different components. Each of these components wasoriginally under the ownership and control of a single telephone serviceprovider. Currently, however, respective components in the PSTN may beowned and/or under the responsibility of different parties. For example,a long distance telephone company may be responsible for long distancelines, whereas a local telephone company may be responsible for locallines, and a subscriber may be responsible for equipment at thesubscriber premises.

[0003] When a malfunction in the PSTN arises, it is necessary toidentify whether the malfunction is due to a problem located at thesubscriber premises, in the subscriber loop or in the network of achosen service provider. Responsibility for correcting the problem lieswith the party responsible for the component where the problem lies.Matters are complicated by multiple service providers competing forlocal telephone communication services. As a result, the subscriber loopmay be owned and maintained by one company yet leased by another companythat provides local services to subscribers. Hence, each local serviceprovider needs a way to immediately test for proper functioning of thenetwork as far as a network interface device (NID). The NID ispositioned at the DEMARC, i.e., the demarcation point where a localtelephone company responsibility stops and the subscriber responsibilitybegins. Typically, the NID is located either adjacent to a subscriber'spremises or a short distance away from the subscriber's premises. Thus,there is a need to be able to determine the location of a problem withinthe PSTN without incurring significant overhead and without sufferingsubstantial delay.

SUMMARY OF THE INVENTION

[0004] The present invention addresses limitations of the conventionalsystem by providing a remotely activated test unit at a NID. The testunit can perform a number of different tests to identify malfunctionsand to determine the location of problems. For example, the test unitmay be able to generate tones, silence a line and identify latency fortransmitted signals. The test unit may be remotely activated toeliminate the need for sending maintenance personnel out to the NID.

[0005] In accordance with one aspect of the present invention, acomponent for testing a portion of a network is provided in a NID. Thecomponent includes a testing module for performing testing on a portionof the network as well as an activation module for activating thetesting module to perform the testing. The activation module includes aremote activator for remote activation. The remote activator may takethe form of a tone detector for detecting a characteristic tone or aradio frequency detector for detecting at least one characteristic radiosignal for activating the testing module. The testing module includes atone generator for generating a test tone. In addition, the testingmodule includes a silencing element for silencing a portion of thenetwork or a loop-back element for echoing signals over a portion of thenetwork.

[0006] In accordance with a further aspect of the present invention, asystem is provided in a communications network that providescommunications with customer premises. A network includes a localexchange carrier wiring. The system includes a NID for providing aninterface between local exchange carrier wiring and customer premises.The system also includes a testing device for testing a portion of thenetwork terminating at the NID.

[0007] In accordance with an additional aspect of the present invention,a test unit is positioned at a NID within a communications network. TheNID is in proximity to subscriber premises. The test unit is operativeto test at least a portion of the communications network. The test unitincludes at least one element for initiating such a test.

[0008] In accordance with a further aspect of the present invention, acommunications network includes a NID. Tests are performed with a testunit at the NID to determine whether the communications network isrunning properly and whether any problems exist in the communicationsnetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] An illustrative embodiment of the present invention will bedescribed below relative to the following drawings.

[0010]FIG. 1 is a diagram depicting connections between a centralswitching office and a subscriber's premises.

[0011]FIG. 2 is a diagram depicting major components utilized in theoperation of a subscriber loop between a central switching office and asubscriber's premises of FIG. 1.

[0012]FIG. 3 is a diagram depicting in more detail components employedin a network interface device and subscriber premises.

[0013]FIG. 4 depicts a test unit in an illustrative embodiment of thepresent invention.

[0014]FIG. 5 is a flow chart that provides an overview of the stepsperformed to complete testing in the illustrative embodiment.

[0015]FIG. 6 is a diagram illustrative of a logical component of thetest unit.

[0016]FIG. 7 is a flow chart illustrating the steps that are performedduring a tone test.

[0017]FIG. 8 is a flow chart illustrating the steps that are performedin silencing a phone line by a test unit.

[0018]FIG. 9 is a flow chan illustrating the steps that are performed toloop-back a signal by a test unit.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The illustrative embodiment of the present invention includes atest unit at a network interface device (NID). The positioning of thetest unit at the NID enables testing to determine whether the problemresides at a given subscriber premises or in other portions of thecommunications network. The test unit can perform a number of differenttests to determine whether portions of a communications network areoperating properly. The test unit is remotely activated. It can beactivated, for example, by sending a characteristic radio frequency (RF)signal pattern or a characteristic tone sequence.

[0020]FIG. 1 depicts a portion 100 of a communications network between acentral switching office 102 and subscriber premises 104 and 106. Thesubscriber premises 104 and 106 may be a home, an office or otherfacility in which a telephone set is present. Each of the subscriberpremises 104 and 106 includes respective telephone sets 110 and 112.Copper wires 114 and 116 connect the telephone sets 110 and 112 torespective NIDs 124 and 126.

[0021] External telephone lines 120 extend from port card 122 at thecentral switching office 102 to the NID 124. Similarly, externaltelephone lines 118 extend from port card 125 to NID 126. Port cards 122and 125 connect telephone lines with a central office switch 108. Theswitch 108 is responsible for switching calls to appropriatedestinations. The switch 108 may effect an electrical connection betweenport card 122 and port card 125 to establish an end to end telephoneconnection between telephone 110 and telephone 112.

[0022] The “subscriber loop” between central switching office 102 andcustomer premises 104 is formed by the set of wires and connections thatrun between the port card 122 and the telephone set 110. The “subscriberloop” between the central switching office 102 and the customer premises106 is formed by the set of wires and connections extending from portcard 125 to telephone set 112.

[0023] Those skilled in the art will appreciate that the depiction ofthe communication network 100 shown in FIG. 1 is a somewhat simplifiedview of a typical communications network. Additional components may becontained within the communications network 100. Moreover, theorganization of the communications network may differ from that depictedin FIG. 1. The depiction in FIG. 1 is intended to be merely illustrativeand not limiting of the present invention.

[0024]FIG. 2 depicts components in the central switching office 102 andsubscriber premises (in this case, subscriber premises 104), that areused during normal operation of a telephone subscriber loop. Thesubscriber loop extends from port card 122 at the central switchingoffice 102 through external telephone lines 120 and through NID) 124.The central switching office 102 includes a ground 206 and a DC powersource, such as battery 204. The battery 204 may provide a specifiedpotential, such as 48 volts. The battery 204 drives current around thesubscriber loop whenever the circuit (described in more detail below) isclosed by effecting connection between the external telephone lines 120that run through the NID 124. A switch 214 is provided at the subscriberpremises 104. The switch 214 is open whenever a telephone (includingearpiece 210 and mouthpiece 212) is “on hook” (e.g. when the telephonehandset is resting on the cradle). The switch 214 is closed when thetelephone is “off hook” (i.e. when the handset is not resting in thecradle). The closure of the switch 214 effects the closed circuitbetween the battery 204 and the ground 206 at the central switchingoffice 102. As a result, a potential voltage is created that issufficient to drive currents carrying voice (e.g. conversations) anddata signals over the telephone lines 120. When switch 214 is open (i.e.the telephone is on hook), DC potential voltage on the subscriber loopis still there, but no current can flow.

[0025] When a call arrives at the central switching office 102 to beconnected to a telephone that includes earpiece 210 and mouthpiece 212at the subscriber premises 104, the central switching office takes stepsto signal the need for the subscriber to answer the phone. The signalingis done by means of a ring generator 202 and a ring detector 208. Aswitch 222 connects the ring generator 202 with port card 122. Whenswitch 222 is closed, an alternating current is generated by the ringgenerator 202 and placed onto the telephone line 120. The ring detector208 recognizes the alternating current, and generates an audible ringsignal at the subscriber premises 104. When the subscriber hears thetelephone ring, the subscriber answers the telephone, resulting in theopening of the switch 222 and the removal of the alternating currentfrom the subscriber loop. When the telephone call is completed, switch214 is opened to remove the voltage potential across the telephone lines120. Capacitor 216 isolates the ring detector 208 from the DC subscriberloop, so that the ring detector can be activated only by alternatingcurrent.

[0026] Against the above-described background, the operation of the testunit may be better understood. As shown in FIG. 3, the test unit 304 ispositioned in the NID 124 for customer premises 104. For the portion 100of the communications network depicted in FIG. 1, the NID 126 andcustomer premises 106 may have similar configurations to NID 124 andcustomer premises 104, respectively, depicted in FIG. 3. In fact, eachNID within a communications network may optionally include such a testunit.

[0027] As shown in FIG. 3, the NID 124 includes an activation signaldetector 306. This activation signal detector 306 detects a distinctsignal for activating the test unit 304. The distinct signal may beremotely generated and sent over the telephone lines 203 to the detector306. The distinct signal may be transmitted from a transmitter 207,shown in FIG. 2, at the central switching office 102, which attaches toport card 122 as the ring generator 202 via switch 222. In oneembodiment, the signal from the central switching office 102 is alow-level radio frequency signal. The preferred signal is the 20-25 kHzrange in a band that is not allocated for commercial broadcasting.Nevertheless, those skilled in the art will appreciate that other bandsmay be used and that different distinct signals may be used to practicethe present invention. The activation signal detector 306 may beimplemented as the detector of the designated radio frequency via aphase locked loop tone detector. Capacitor 320 isolates the activationsignal detector 306 from the rest of the subscriber loop. Resistor 322assures that current does not flow into the activation signal detector306 when the A/C ring signals are transmitted to the subscriber premises104.

[0028] The NID 124 includes an off hook detector 307. The off hookdetector 307 detects the increase in DC voltage that occurs when thetelephone at the subscriber premises 104 goes off hook. The off hookdetector 306 communicates the change to the off hook state to the switch308. Those skilled in the art will appreciate that a number of differenttypes of electronic modules may be utilized to implement the off hookdetector. There are a number of off-the-shelf commercially availablemodules for implementing such functionality.

[0029] The NID 124 contains a standard current limiter 310. The currentlimiter 310 is tied to ground and provides protection against surges ofelectricity on the external telephone lines. The current limiter 310 maytake the form of a fuse, an electronic surge protector or a ground shuntthat automatically opens the subscriber loop circuit or runs the currentground when the voltage on the telephone line exceeds a threshold.

[0030] Switch 308 controls the behavior of the test unit 304. If the offhook detector 306 detects an off hook condition, the test unit 304 isdeactivated by opening switch 308. Switch 308 is also controlled byinput from the activation signal detector 306. The activation signaldetector 306 will close the switch (presuming no off hook signal hasbeen detected) when the activation signal is detected. Those skilled inthe art will appreciate that a number of commercially availablecomponents may be utilized to implement switch 308.

[0031] The test unit 304 may be implemented using differentalternatives. FIG. 4 depicts a preferred alternative where the test unit304 is implemented as a special purpose microcomputer 400. Themicrocomputer 400 boots up anytime there is a non-negligible voltagebetween contact points 312 and 314 (see FIG. 3). The microcomputer 400includes a microprocessor 402 and storage 404. The storage may includeboth primary and secondary memory and may include computer-readablemedia, such as optical disks, magnetic disks and the like. The storage404 holds both data 406 and computer instructions 408. The data 406 andinstructions 408 are used to implement the various tests performed bythe test unit 304.

[0032] Those skilled in the art will appreciate that the test unit 304may be also be implemented using dedicated electronic circuitry. Thetest unit 304 need not be implemented as a microcomputer. The test unit304 may be implemented as servo-activated telephone response module,implementing functionality such as that described in co-pendingapplication entitled “Interactive Telephone Response Module” which wasfiled on Feb. 5, 1998, application Ser. No. 09/019,323, which isexplicitly incorporated by reference herein. Moreover, computing systemsother than microcomputers may be utilized for implementing the test unit304.

[0033]FIG. 5 provides a flow chart of the steps that are performedduring testing. Initially, the test unit 304 is activated by sending anactivation signal from the central switching office 102 toward thesubscriber premises 104 (step 502 in FIG. 5). As was mentioned above,the activation signal is detected by activation signal detector 306. Theactivation signal detector 306 generates an output that closes switch308 so that the test unit 304 becomes active. The test unit 3041isalready running because of the presence of a voltage across end points312 and 314. The test unit 304 then initiates one or more tests toidentify the presence of problems within the telephone network and toidentify the location of the problems within the telephone network (step504 in FIG. 5). When the testing is completed, the test unit 304 may bedeactivated by opening switch 308 (step 506 in FIG. 5).

[0034]FIG. 6 depicts the logical components of test unit 304. The testunit 304 includes a tone generator 602 for the generation of one or moretones for transmission over the communications network. FIG. 7 is a flowchart illustrating the steps that are performed during a tone test inwhich one or more tones are generated by the tone generator 602.Referring to FIG. 7, initially, a tone is generated at a first test unitwithin the communications network (step 702 in FIG. 7). The tone may,for example, constitute a sinusoidal signal with a predeterminedamplitude and frequency. The tone is then transmitted to a second testunit position within another NID, where the tone is received (step 704in FIG. 7). The second test unit compares the generated tone with thereceived tone to identify the extent of line loss over the line thatconnects the two test units (step 706 in FIG. 7).

[0035] The test unit 304 also includes a silencing element 604 as shownin FIG. 6. The silencing element 604 is used to silence a portion of thecommunications network. FIG. 8 depicts steps that are preformed in usingthe silencing element 604. A first test unit remains quiescent (step 802in FIG. 8). While the first test unit is silent, a second test unittakes measurements (step 804 in FIG. 8). These measurements may includea measurement of line noise or echo path delay, for example.

[0036] The test unit 304 may also include a loop-back element 606. Theloop-back element 606 seeks to return signals in the form in which theywere received. FIG. 9 provides a flow chart of the steps that areperformed using such a loop-back element 606 to perform a test by thetest unit. A first test unit transmits a signal to a second test unit.The signal is received at the second test unit (step 902 in FIG. 9). Thesecond test unit transmits the signal towards the first test unit suchthat the signal is in the same form and at the same level (step 904 inFIG. 9). In other words, the second test unit seeks to echo the signalback towards the first test unit that generated the test signal. Thesignal is received at the first test unit (step 906 in FIG. 9), and thefirst test unit records the time at receipt of the signal so that theroundtrip signal delay may be measured (step 908 in FIG. 9).

[0037] The test unit 304 may include a number of other different typesof elements. The logical components 602, 604 and 606 depicted in FIG. 6are intended to be merely illustrative and not limiting of the presentinvention. For example, the test unit 304 may include components forplaying or for recording and analyzing digitally encoded voice data. Itmay also include capabilies to play or record and analyze digitallyencoded signals representing semantically-encoded waveforms designed totest transmission and receipt of data over acoustic data links ordigital subscriber links in the manner taught in U.S. Pat. No.5,748,876, entitled, “System and Method For Testing Acoustic Modems WithSemantically Encoded Waveforms, issued on May 5, 1998, which isincorporated by reference herein. Furthermore, the test unit 304 mayinclude an acoustic data link with a remote test device for transmittinginstructions and data to the remote test device. This acoustic data linkmay be used to send signals to play and record signals to receiveprocessed data from the remote test device.

[0038] While the present invention has been described with reference toan illustrative embodiment thereof, those skilled in the art willappreciate that various changes in form and detail may be made withoutdeparting from the intended scope of the present invention as defined inthe appended claims.

What is claimed is:
 1. In a communication network for providingcommunications with customer premises, and said network including localexchange carrier wiring, a system comprising: a network interface device(NID) for providing an interface between the local exchange carrierwiring and the customer premises, said network interface device furtherincludes: a switch; an off-hook detector to detect use of thecommunication network at the customer premises; and a testing device fortesting a portion of the network and terminating at the NID, the testingdevice including a silencing element for silencing the portion of thenetwork, wherein said off-hook detector opens said switch to deactivatesaid testing device.
 2. The system of claim 1, wherein the testingdevice includes a remote activation module for remote activation of thetesting device to perform tests.
 3. The system of claim 2, wherein theremote activation module includes a tone detector for detecting at leastone characteristic tone for remote activation of the testing device toperform tests.
 4. The system of claim 2, wherein the remote activationmodule includes a radio frequency detector for detecting at least onecharacteristic radio signal for remote activation of the testing device.5. The system of claim 1, wherein the testing device includes a tonegenerator for generating a test tone.
 6. The system of claim 1, whereinthe network is a telephone network.
 7. The system of claim 1, whereinthe portion of the network is quiescent.